1. Field of the Invention
The present invention relates to a planar antenna for moving objects which employs a microstrip antenna and which is well suited for installation on a moving object such as a vehicle.
2. Description of the Prior Art
With antennas heretofore used on vehicles such as automobiles (e.g., antennas for personal two-way radio, FM radio, etc.), the antenna directivity is preferably selected such that the antenna is omnidirectional in a horizontal plane and the beam is concentrated in a horizontal direction in a vertical plane and the long rod antenna is mounted on the vehicle body. Thus, there are problems during, for example, the running, garaging and washing of the vehicle.
On the other hand, as disclosed for example in JP-A-No. 56-715 for an "automobile antenna", a microstrip antenna has been proposed which is so constructed that it is small in size, light in weight and low-profile and this construction not only overcomes the foregoing deficiency but also is suited for mounting on a vehicle. When the antenna is excited in the ordinary feeding mode, however, it radiates radio waves in a direction vertical to the antenna surface.
As a result, where the above microstrip antenna is simply mounted on the surface of a vehicle such as an automobile, its directivity is confined in a particular direction. Thus, when using the antenna for signal transmission and reception in a radio system such as a personal two-way radio system or FM radio requiring a horizontal directivity, the antenna must be inclined from the horizontal plane by a given angle to effect the transmission and reception in the horizontal direction. And yet, in that case, the use of the single antenna gives only one directivity in a particular direction and thus there are disadvantages that a plurality of the microstrip antennas must be combined so as to obtain the desired omnidirectional directivity in the horizontal direction and in that the combined antenna height is also increased.